Currently, the standard of the Blu-ray Disc™ using a blue purple semiconductor laser allows an optical disc for the public having recording density of substantially 100 GB to be commercialized. Henceforth, an optical disc having high capacity which exceeds 500 GB is desired. However, a new technology of realizing high density, which is different from the technology of realizing high density by using short wavelength and high NA of an objective lens in the related art, is required in order to realize such an ultra-dense optical disc.
Research relating to a next-generation storage technology has been performed and a hologram recording technology of recording digital information using holography attracts attention. An example of the hologram recording technology includes JP-A-2004-272268 (PTL 1). This publication discloses a so-called angle multiplexing type in which data of pages which are different from each other is displayed in a spatial light modulator and multiplexed recording is performed while an incident angle of a reference beam to an optical information recording medium is changed.
An example of a technology of optimizing a reference beam angle includes JP-A-2011-227967 (PTL 2). This publication discloses that “a photodetector detects diffraction light which is diffracted by irradiating an optical information recording medium in which information is recorded, with an adjustment beam having the same amplitude distribution and phase distribution as those of at least some of signal beams in recording and diffraction light and an angle of causing the reference beam to be incident to an optical information recording medium is controlled based on detected information.”